As discussed in this FFT's thread, over time, very small perturbations in the orbit of Uranus were measured, allowing the discovery of Neptune. Without computers, to emphasize. The amount of data and the time span required amazes me. It was nearly impossible to accomplish this feat. Yet, humanity's brightest minds managed. So I often say "Anything is possible if you try hard enough". This is why I don't consider even faster than light travel impossible right away. But I ran into trouble when I did the math about just how fast could a power-hungry civilization spread if it desired to. Stupidly quickly compared to how long the universe is around!

How long would it take for a hypothetical FTL-capable civilization to take over an entire spiral galaxy, or the observable universe?

Let's assume that there are 40 billion Earth-like planets in the Milky Way (Which has 250 billion stars) and 1.6*1023 in the observable universe (1024 stars according to a high estimate - Answer 5). I assume the growth of said civilization to be exponential. I think of the speed of the FTL travel as limitless for the purpose of my thought experiment. I do not account for the time and effort required to actually advance technologically to superluminal travel, nor do I think about how long would it take to build spaceships to move the inhabitants around.

At first, let's restrain the aliens a bit. Atmospheric composition suitable for the aliens is uncommon in the universe, therefore, habitable planets are not readily available and the aliens require terraforming to gain new living space. (For now, let's not consider cyborgs or others 'easier' ways around). Let's also take into account the time required to terraform a single world - 100000 years (I read that it would take that long to make Martian atmosphere breathable). So we add a new world for every already inhabited one, once every 100 millennia. I calculate the growth rate from here and then use Desmos to get the results.

So, after 100000 years, the civilization inhabits 2 planets, 4 planets after 200000 years, 8 after 300000 and so on. They would get to live on the 40 billion planets of the Milky Way in 3.522 million years. It would take them 7.708 million years to take over the observable universe! Biologically, they could still be considered one species all around even despite living on all these different worlds. Why? Firstly, FTL travel, which I believe speaks for itself, gene pool would be mixing thoroughly. Secondly, doubling the population in 100000 years would require extremely strict and precise reproduction control with the resulting growth rate infinitesimal in comparison to our own. Considering this scenario, the civilization would spread across the observable universe in 1/1790 of it's measured age! Mind you this is the slowest scenario I am playing with.

*Second scenario with a population growth equal to the current growth of human population. Imagine that the civilization overcame the hostility of the universal environment (cyborgs, insanely quickly terraforming, or genetic engineering to allow adaptation instead...). The civilization would control two planets in just 63.7 years and it would double again in the same time. This leads to a galaxy-spanning civilization in just 2245 years and to an universe-wide one in 4913 years, which already seems very far fetched and unbelievable.

*Third scenario, let's exaggerate absurdly. We now have a bacteria/nanobot like growth rate doubling the numbers every 15 minutes! I assume uninterrupted spread. A galaxy would fall in 8.8 hours, the universe in 19.27 hours. This scenario looks like an ultimate doomsday AI superweapon unchained. Such destruction engine would be slowed down very little however, by consuming raw materials, not just occupying planetary surfaces. Imagine the Stargate replicators literally eating away planets.

*Note: I count with Earth-like planets only, which probably would not matter if you could colonize basically everything solid. I do not think a difference of even multiples of the calculated time matters on the universal scales.

Even if I only consider the "100 millennia to double" scenario, the time for a single civilization to assume control over the entire observable universe and beyond is so minuscule compared to the age of the actual universe. I propose a few solutions to my dilemma, but it smells like Fermi paradox tweaked and according to Drake's equation, the number of civilizations in the universe should be staggering, regardless what variables we do the math with. So where is everybody?

1) FTL travel is not possible. Simple as that.

2) FTL civilizations don't exist. Less advanced civilizations don't get past the great filter, succumbing to the internal struggles we face on Earth today. If life in basic principles works the same as on our piece of rock (survival of the fittest), then I am afraid that extraterrestrial life would be territorial, power-mongering and domineering, both internally and externally to other aliens. If FTL was as easy as to allow aliens to spread faster than evolution could rid them of the aforementioned animal traits, they would just bring the problems of their home world out into space with them.

3) Which brings us to another possible solution. There may be countless FTL-capable civilizations, which wage wars of hardly imaginable proportions among each other, throwing death stars at one another as if they were merely cannon fodder. This would definitely slow their expansion rate, since it would not be safe to spread and no aliens would be able to reign across the universe.

4) The universe is radio-silent because if civilizations were capable of FTL travel, they would most certainly be capable of FTL communication. EM spectrum would be ridiculously ineffective and slow as means of communication.

5) Universe may be full of life and chaotic, but we don't matter, so they ignore us, which goes hand in hand with point 4. We are unable to communicate with them and vice versa.

That's very interesting An'shur. I'm very skeptical with FTL travel been possible at all but expansion rates are an interesting topic in relation to all the speculative field of the Fermi paradox. I'm also very skeptical of extraterrestrial intelligence at all.

I like the fact you thought about a self regulating mechanism for those brutal expansion rates (war in this case) It reminded me of the analog speculation on the sub-lumial travel;

It has been shown in some papers that the colonisation of the entire galaxy can be archived at only 10% the speed of light within 5.000.000 years using fair assumptions on the population growth and emigration rates. Consider the fact that the Milky Way is at most 11 billion years old. The conquer of the galaxy then is surprisingly quick even for colonial expansions way below the speed of light. Consider also the fact that the galaxy is 100.000 light years across at least (the diameter of the disc). We would be able to arrive to every single system in just 50 times the duration of the voyage of a photon in straight line from one end to the other. Two alien species (one in the other side of the disk and one in the core of the galaxy) would only be able to exchange 50 question-answer messages before the invasion of the galaxy was completed (if they are lucky enought to spot the start of the expansion since the beginning).

There has been some objections to this crazy expansion rate (which I think could be appliet also for your FTL-travel scenarios). It has been shown that only a society that has economic (and ecological) sustainability, with a strict birth control policy and a coherent cautios long term expansion strategy can really accomplish the colonisation of the galaxy. It has also been shown that a society that don't make control policies on its growth would exponentially consume more materials that those available in the increasingly large territory they expand on due to the limits of light speed travel. This would generate in a few millenia an interstellar societal collapse that would limit the "expansion bubble" to a few tenths of light years in what has been called the "ligth cage". So the reality is that no colonisation would occur in 5 million years (at those speeds they would fall in a Malthusian catastrophe quickly and would be limited to a tiny region of the galaxy). Only a very slow and gradual attempt would be victorious in invading the entire galaxy.

But if we need 5 million years at least, and probably many many times that time to conquer the galaxy, there are other important issues. Political issues in fact. As the different systems get economically independent (if not it would be a total economic waste; try to picture a "central system" sending food and resources to far away colonies when they could gather those themselves) and confront diverse materialistic conditions because of diverse geopolitical, economic and historical situations across the galaxy, it is fair to assume that a common well organized and controlled project would fall appart quickly. Just imagine humanity having a strict plan for any project conceivable for more than a few millenia (maybe the Catholic church could be the best candidate for that). Would you think that this could be continued in time 10 times more? 100 times more? 1000 times more? for a territory that has to communicate and execute law-enforcement across vasts amounts of space? if a colony revolts and strikes against the rest of the "empire" how many thousand years they would have to wait for the arrival of any reasonable coercive task-force (maybe the task-force itself would lose any historical and political connection to the law of the empire, they would lose their lives and the ones of their children across centuries to arrive to the other planet; a planet where no revolutionary group would be waiting and a new status quo might have been established long ago and even fall apart and restablished across several generations). This is assuming very human behaviour with very human lifespans but what about an alien civilization? I don't really think even they would be able to mantain a coherent political frame and planning across those distances and geological time-scales. And remember, our best bet is a sustainable society with very strict (probably planned and counscious) control on its growth! Even if they had the mindset of ants and where extremely obedient and collectivists in their political aproach I think they would end up diversificating becuse of the time and space involved. A bunch of ants left alone a kilometer away from their colony would die or create their own with the local resouces available, but they would certainly wouldn't keep a stable relationship with the colony mantaining loyalty to something that they would never see present in their daily problems. The size of the Milky Way and the speed limit imposed by nature is a killer for any joint efforts, fluid communications, transportation etc... All fundamental issues for the mantainance of a unitary sociaty or any empire we have known.

But now comes the interesting thing. What if political hegemony is not needed for the expansion? Well here comes the old idea of self-replicating Von Neuman probes; machines that are capable of interstellar travel, data collection, resource identification, resource exploitation, self reproduction and targeting of other systems. That indeed would be a very feasible strategy for any advanced species (we are creating the first 3D printers that are able to print all their components so it maight be eventually possible even for us to build somethign like this). Von Neuman probes would have little interdependece if well programmed; even the civilization that created them could be long extint before they colonise the galaxy or at least they could perfectly forget about this project so no actual political continuation is needed. I would reccomend this paper if any of you want to read about this concept.

Finally there's this amazing read (I'm sometimes amazed by the fact these are scientific publications). They create a mathematical model for Von Neuman self-replicating probes expansion in the galaxy. Their main point is that even the most efficient self-replication would have enginering error porpagation. If billions of probes are created across millenia of expansion it is fair to assume that some of the porbes would copy themselves with malfunctions of some sort (in their code or in the hardware). In general those mutant probes would have disfunctionalities and would be unable to get to another system, but in some cases the mutations would be functionally advantageous. Self-replication, mutation and time is all that you need to see Darwinian evolution by natural selection. Some probes might lose their exploratory behaviour and gain new goals. And the key idea here is that some probes might become so different as to show signs of speciation between Von-Neuman probes. A true self-replicating spacecraft ecology could arise and even a food chain where Von-Neuman probe predators hunt for the other probes (easier than gathering the resources to build a next generation yourself) could apear. That in turn would damp the growth and expansion. They have simulated some scenarios like this using percolation theory and have shown that the predator and prey behaviour could in fact limit the expansion to a very small sector of the galaxy (worst cases when the expansion starts close to the end of the disk since the prey get confined quickly). An equilibrium is the reached where predators and preys travel between the stars limiting each other by means of hunt and food deprivation.

There's one possible problem to interstellar travel. Dust. Interstellar dust is extremely sparse, but given the distances and the great travel speeds, could it pose a problem? Has anyone tried to calculate the risks? A small pebble, even just a gramme, will utterly destroy your spacecraft hits it at 10% the speed of light. That's nearly half a gigajoule of energy, or the equivalent of more than 100 tonnes of TNT. Hare are a couple of videos illustrating that kind of energy if absorbed by the spacecraft:

Source of the post 4) The universe is radio-silent because if civilizations were capable of FTL travel, they would most certainly be capable of FTL communication. EM spectrum would be ridiculously ineffective and slow as means of communication.

That's how it is in Star Trek, they use extra-dimensional space to communicate and if you have FTL travel you can probably crack FTL communication. There was a paper I read before about sending compressed FTL messages in pulses through distorted space, will have to see if I can locate that.

They create a mathematical model for Von Neuman self-replicating probes expansion in the galaxy

An'shur wrote:

Source of the post We now have a bacteria/nanobot like growth rate doubling the numbers every 15 minutes!

What we are all forgetting here is that self-replicating machines (especially in swarms) cannot replicate exponentially (or even at the speed a lot of people think they can). There is a hard limit to how fast you can do something without causing so much friction that you just explode. Complexity as you might find in such nano-swarms will require a fair bit of energy to replicate. Complexity also will cause the machine to take longer to self-replicate, unless they replicate faster, which would then make them explode again. But the idea of self-replicating swarms is very complex and more then we are asking for here. Suffice to say it is not possible to colonize the entire universe (I know it was an exaggeration An'shur) with them. There are extremely intricate engineering hurdles to overcome even if they are tasked with just traveling around a few light-years and terra-forming and/or exploring and passively replicating. But we were talking about FTL here, so to continue:

For the sake of argument, FTL is possible. You just need to be inventive about it and read between the lines of your physics textbooks. The Alcubierre drive is proof of this. Its dynamics do not violate general relativity. Yes there are those 'minor' complications like requiring negative mass and so on, but certain designscan minimize the requirement. My point here is that the laws of physics do not say you cannot travel faster then light. The term itself is a misnomer anyway. It is the maximum speed at which massless particles (including photons, but also gluons and theoretical gravitons) can travel to maintain electromagnetic casualty between points in the universe as determined by the Lorentz Transformation in relation to the famous Maxwell equations of field electromagnetism. I would suggest to anyone wanting to understand this type of things to learn more about the work of Lorentz, Maxwell and other pre-Einsteinian physicists (maybe not you guys on this forum, you seem to know a lot about this science ).

Naturally, to go faster then other matter, you must have negative matter or negative mass. No Mass (or neutral mass) = limit of casualty, and (positive) mass = impediment to motion. It stands to reason that negative mass is the opposite of positive mass and makes things go faster then mass-less matter, which acts as a speedometer in this case. Essentially the only thing standing in our way of building a Alcubierre warp-ship is this negative matter. For the moment we will ignore the other complications that will arise as a result of FTL travel like paradoxical phenomena. We can`t find negative matter, don`t know how nature could make it now and we cannot manufacture it like we can heavy elements.

An'shur wrote:

Source of the post 2) FTL civilizations don't exist. Less advanced civilizations don't get past the great filter, succumbing to the internal struggles we face on Earth today. If life in basic principles works the same as on our piece of rock (survival of the fittest), then I am afraid that extraterrestrial life would be territorial, power-mongering and domineering, both internally and externally to other aliens. If FTL was as easy as to allow aliens to spread faster than evolution could rid them of the aforementioned animal traits, they would just bring the problems of their home world out into space with them.

3) Which brings us to another possible solution. There may be countless FTL-capable civilizations, which wage wars of hardly imaginable proportions among each other, throwing death stars at one another as if they were merely cannon fodder. This would definitely slow their expansion rate, since it would not be safe to spread and no aliens would be able to reign across the universe.

5) Universe may be full of life and chaotic, but we don't matter, so they ignore us, which goes hand in hand with point 4. We are unable to communicate with them and vice versa.

These are probably the most likely, just based off of what we know about our universe. I omitted point 4 because it is only partially correct. I said earlier that we would ignore the actual effects of FTL travel. Now I would like to address it here in relation to your fourth point.

DoctorOfSpace wrote:

Source of the post An'shur wrote: 4) The universe is radio-silent because if civilizations were capable of FTL travel, they would most certainly be capable of FTL communication. EM spectrum would be ridiculously ineffective and slow as means of communication.

That's how it is in Star Trek, they use extra-dimensional space to communicate and if you have FTL travel you can probably crack FTL communication. There was a paper I read before about sending compressed FTL messages in pulses through distorted space, will have to see if I can locate that.

As mentioned earlier, the speed of light is actually the maximum speed at which points in the universe can `communicate` (i.e. maintain casualty) to each other, and be seen communicating to one another by any other point in the same universe. As soon as one area of the universe (say, a space ship) transcends that speed (going faster then mass-less matter), it starts to `communicate` backwards in time relative to it`s origin and it`s relative speed. If the space-ship travels twice the speed of light (2c), to a destination 2 light years away from its origin, but then travel an extra year beyond that point from its origin`s point of view, beaming out homeward-bound messages, at some point these start arriving at its origin before the ship was even launched! This would be.. interesting to say the least. You could plan out entire expeditions via listening to the reports of your future self aboard the ship. Cool. All right maybe not, because this would cause paradoxes and all those bad things that you see happen in time travel movies will happen to you. The very fact that mass-less particles exist as the limit to casualty in the universe suggests that the laws of physics convene to prevent such disastrous things from breaking spacetime. The weird thing is that the messages sent from the traveling space ship in the example are not being sent FTL, they would be relativistic, at the speed of c. If you want to know how terrible FTL communication would be, check out the Tachyonic anti-telephone thought-experiment devised by Einstein and Arnold Sommerfield and later explored by Richard Tolman in his Tolman`s Paradox.

So I would think that communications at interstellar distances would need to be delayed or sped-up en route after being sent to their destination relative to their origin`s position and velocity in timespace to arrive instantly. I don`t know how this could be done.

After all that is said and done, EM might be the only medium in which to communicate effectively - unless the aliens use hypothetical means like neutrinos, quark entanglements or something even more exotic and fantastic that does not lead to paradoxes. But even if the majority of them would use such strange and to us, undetectable ways of talking, there would be those who inevitably do not for whatever reason. We should be able to pick those up at some point. And is my point: we have not been looking for long enough or hard enough to really make dent in this field. That is the attitude of SETI, and although it implores you to ``keep faith``, its really all you can do. Unless you want to be more pro-active and send out messages yourself. We did that a few times and none of them repeated, so I guess those are just another WOW! signal for somebody else.

FastFourierTransform wrote:

Source of the post There has been some objections to this crazy expansion rate (which I think could be appliet also for your FTL-travel scenarios). It has been shown that only a society that has economic (and ecological) sustainability, with a strict birth control policy and a coherent cautios long term expansion strategy can really accomplish the colonisation of the galaxy. It has also been shown that a society that don't make control policies on its growth would exponentially consume more materials that those available in the increasingly large territory they expand on due to the limits of light speed travel. This would generate in a few millenia an interstellar societal collapse that would limit the "expansion bubble" to a few tenths of light years in what has been called the "ligth cage". So the reality is that no colonisation would occur in 5 million years (at those speeds they would fall in a Malthusian catastrophe quickly and would be limited to a tiny region of the galaxy). Only a very slow and gradual attempt would be victorious in invading the entire galaxy.

Yes, exponentiation tends to be blunted by other overlapping internal systems that arrange for self-regulation. Just take the population crises for example. A few decades ago scientists believed that the population boom of the industrial revolution and exponential growth thereof in the West and in Asia would doom us all to die from over-population difficulties by the 2050s, when humans would number over twenty billion. Now it has been learned that because of the development of first world countries, birth-rates in those countries has dropped. Population growth stabilized. Now the only human growth is from 2nd and 3rd world countries - but the reason why it is from there is because they are making the same industrial-era transition that the first-world countries made. After they pull through and provided we can clean up this planet and curb our excessive consumerist mindset, the population should stabilize overall at around 12 billion. Still a lot people, but technological and sociological innovation that results from the the prevalence of education in developed countries (which will be the ONLY countries by then mind you) should make that sustainable.

Anyway, to tie into what you said here about gradual colonization, I remember reading in Carl Sagan`s book Cosmosthat based on the expansion dynamic`s of civilizations here on Earth, if a alien civilization 200 light-years away from Earth using sub-light travel started colonizing the stars around them, only targeting those stars that are suitable for them (Sagan used yellow dwarf stars as an example) in a roughly spherical volume, they would take 2 million years to reach our solar-system with their scouts, assuming they did not make Sol an objective in their missions. A million years per hundred light years. 2 billion years for the entire galaxy (which, as of new research, is around 170,000 light-years across). Bear in mind this is if they only colonize type G yellow dwarf stars.

The take away from all of this is that interstellar expansion is fiendishly difficult even with FTL. It is not a game changer, despite getting so much attention.

midtskogen wrote:

Source of the post There's one possible problem to interstellar travel. Dust. Interstellar dust is extremely sparse, but given the distances and the great travel speeds, could it pose a problem? Has anyone tried to calculate the risks? A small pebble, even just a gramme, will utterly destroy your spacecraft hits it at 10% the speed of light. That's nearly half a gigajoule of energy, or the equivalent of more than 100 tonnes of TNT.

At subrelative speeds, even the hydrogen gas is deadly. It depends what your space craft is made out of. You would obviously have a curved shield of some strapped on the front of your ship (which some of the SE ships have, if you are curious). The shields would have to be hard but also rather absorptive and flexible, possibly made out of a aerogel, metamaterial or something similar. As they get bombarded, the shocks of kinetic energy are absorbed and redistributed evenly - maybe even powering internal mechanisms as a opportunistic generator. We must also understand that things in space do not blow up in the same way they do on Earth. Most if not all of the force an explosion makes up there is kinetic and hence easily manageable. Something bigger heading your way would need to be detected beforehand and vaporized by lasers into smaller chunks.

That being said however, At superluminal speeds, nothing will save you (unless you have FTL lasers ). The Alcubierre drive works around this problem because it does not travel through space, space carries it in a bubble of negative matter. Hence gas, dust and bigger chunks might be deflected by the negative matter or even annihilated. I`m not entirely sure what effect a bubble of spacetime would have on a asteroid.

Ahhh, nothing like a FTL alien discussion get those synapses firing ...

I've read through the links and concluded that even though the universe contains virtually limitless amount of resources, a civilization with exponential growth pattern would not be able to sustain itself. We can see it happening with humans. Overabundance of resources would lead to overindulgence, therefore not utilizing said resources to their full potential. Careful, self aware enough civilization could expand across the stars. It's growth would not be exponential, but much slower than I assumed, FTL or not.

Speaking of politics, interstellar or even galaxy-spanning society would be a dictators's worst nightmare. In other words, no galactic empire without FTL travel.

Zoo hypothesis makes sense. I would definitely avoid Earth

Stellarator wrote:

There is a hard limit to how fast you can do something without causing so much friction that you just explode.

I admit my mind has not crossed anything along these lines.

Stellarator wrote:

Alcubierre drive is proof of this. Its dynamics do not violate general relativity. Yes there are those 'minor' complications like requiring negative mass and so on, but certain designs...

Just got a far fetched question (as if warp drive was not far fetched itself): 5m51s, what would happen if you shrunk the field into nothing (doable?) and cut the FTL ship out from the universe? What would happen to it, where would it be? Could it reconnect back to the universe?

I also saw other PBS Space Time's video on superluminal travel, related to FTL exchange of information. But... is it not just a matter of perspective? The narrator says it's not, but also says things like "This seems like a trick, and it sort of is." I still cannot warp my head around it (pun intended), since our FTL ship does not in fact move through space faster than light. Space itself moves, which in my physically uneducated opinion should not cause paradoxes.

Edit: Space is vast. We have detected atmospheres of several extrasolar planets, even discovered what gases are they made of by spectral analysis during transit I suppose. Could we detect oxygen, or in general gases that do not occur without life on Earth sized worlds? I imagine the atmosphere influences the stellar spectra only very faintly. My question is related to the spread of civilizations, sort of. How big or sophisticated a telescope would we require to reliably examine an atmosphere of a planet and conclude there is probably life, depending on the distance of the planet? Would the mirror of the telescope have to be asteroid/city-sized to make the observation across our galaxy? Bigger? Would using many smaller telescopes (interferometry) be better?

Source of the post Speaking of politics, interstellar or even galaxy-spanning society would be a dictators's worst nightmare. In other words, no galactic empire without FTL travel.

Yes and no. You could not even monitor a civilization correctly at those scales in the traditional way governments monitor and steer nations on Earth. So dictatorship and "Empires" in the traditional sense could not exist. They are too reliant on homogenization. Within a interstellar empire (say, 10000 light years across), there would be a very decentralized system wherein solar-systems are united for more or less general goals (such as "establish K2 dominance over the Perseus Arm"). There would very well be a system of government at play there that we could not even fathom, since it operates at timescales and distances measured in tens of thousands of light years. This superposition governance, if it would exist in such a civilization, would be run by AI or cybernetic individuals who measure their lifespans in the hundreds of thousands of years, with spatial comprehension and cognitive abilities to match. They would monitor expansion trends and memetics, and based on the environments of expansion try to make predictions as to how such things panned out, which if accurate would actually portray is happening right at that moment with the civilization in question, thousands of light years away. You would need to make 'Bureaucracy Bots' or AI Gods. If you even wanted that sort of thing.

Interestingly, this would work without FTL. It is just that you would not be unified, since light-lag makes information transfer almost redundant unless the message is timeless in nature and does not require a response. The best you could hope for is a 'trickle effect' wherein news would filter through a web-like hub of short-distance communications channels, eventually spreading throughout the interstellar civilization. At its core, any collection of a thousand or so suns host to members of this civilization would be independent. That's just fine, because if they are emerging at K2 status anyway, they need plenty of room and resources. In this manner, each would beget their own colonial effort, that would expand uniformly until they too hit the horizon for feasible and useful communication, and any colonies beyond that would be on their own, or at least reliant on the more recent, closer established colonies. In sci-fi, this sort of expansion happens with the Tau Empire in Warhammer 40,000. The awesomeness and faulty science of that setting aside, the Tau do not have the FTL technology the other civilizations in the galaxy have, and so colonize the space around them in so-called Spheres of Expansion based off of the previous colonial effort. Its interesting because they are one of the few examples of a subrelativistic alien civilization.

FTL changes this in scale only. You control more, but then you would run into that light cage FastFourierTransform mentioned.

An'shur wrote:

Source of the post Just got a far fetched question (as if warp drive was not far fetched itself): 5m51s, what would happen if you shrunk the field into nothing (doable?) and cut the FTL ship out from the universe? What would happen to it, where would it be? Could it reconnect back to the universe?

In the example given in that video, the ship is not completely disconnected from the universe. It is still connected at a quantum scale. The Alcubierre drive creates a warp in space, a bubble of space/time. By shrinking the space/time bubble, you are not actually shrinking the interior physical volume, just the portion of space it is sitting in. Remember that from the inside of a Alcubierre ship, no matter at what speed you travel at, time and inertia are the same for you even though you are traveling at insane speeds. This is because you are sitting in a little portion of your own space/time. What happens in the outside universe does not effect you - including the outside universe seeing your ship miniaturize. PBS was trying to convey that the more you warp the bubble, the less negative matter you need, to the point you need none, at the extremes of warping: shrinking it to a quantum scale. Sort of hard to explain, because I could not find many references to this phenomena. Bear in mind this warped space may have all sorts of weird side effects, so don't jump into the first warp drive ship you find.

An'shur wrote:

Source of the post Would the mirror of the telescope have to be asteroid/city-sized to make the observation across our galaxy? Bigger? Would using many smaller telescopes (interferometry) be better?

Both are true. With increased sophistication, you could make mirrors that are so perfect that they could have the magnification of Hubble in a scope that could fit in your house. But with telescopes of any type, including those operating on other EM scales (radio, infrared etc), bigger and more of them is better. Since the detection of atmospheric gasses is largely dependent on the planet eclipsing it's star, in order to perform spectrography on all the planets in the milky way, you would need to spread out many thousands of arrays of gargantuan telescopes (thousands of meters across) across hundreds of light years to view transit zones. Again, FastFourierTransform did a terrific post about this sort of thing here. A few Isaac Arthur videos may be interesting in this regard as well:

Source of the post For the sake of argument, FTL is possible. You just need to be inventive about it and read between the lines of your physics textbooks. The Alcubierre drive is proof of this.

How is something that does not exist 'proof' that it is possible? Just because the Alcubierre drive is a solution to the field equations does not mean it is physically valid. It violates several energy conditions and introduces causal paradoxes. Similarly, white holes are very simple to describe in general relativity, but there are deeper principles for why they don't exist.

Source of the post For the sake of argument, FTL is possible. You just need to be inventive about it and read between the lines of your physics textbooks. The Alcubierre drive is proof of this.

How is something that does not exist 'proof' that it is possible? Just because the Alcubierre drive is a solution to the field equations does not mean it is physically valid. It violates several energy conditions and introduces causal paradoxes. Similarly, white holes are very simple to describe in general relativity, but there are deeper principles for why they don't exist.

I'll redefine what I meant. I used the Alcubierre drive as an example that at least mathematically, it is possible to travel faster then light. It is not 'outside' of our mathematical know-how, whereas we have no mathematical basis on how to, say, make a zero-point energy device. The ZPE device is nonscientific because it has no math supporting it's idea of extracting energy from the zero-energy state of matter. The Casimir Effect that ZPE enthusiasts point to would be a measurement of vacuum-state interactions, not energy potential for work. Yes there are other fallacies with zero-point energy, but I use it as an example of what is neither mathematically sound, nor plausible in reality.

An Alcubierre warp-drive is mathematically sound (if you accept Miguel Alcubierre's essentially invented solutions to the physics), but totally unfeasible in reality. Some of those unfeasible items are, but not limited to, those energy conditions and potentially reality-breaking paradoxes you mentioned. Also, how might you shield or divert the tremendous gamma radiation burst caused by the release of trapped matter in the space warp bubble (as explored in this paper)? What effects might actual time travel have on you while you travel through time? And just how on Earth (or elsewhere) are you going to get negative matter?

Questions like these along with those you pointed out are the reason why we might not get our warp-ships for many centuries (or ever). Maybe aliens did crack the FTL dilemma. Probably not. Maybe in the far-future, when civilizations may be far more common in the universe due its great age (if you follow that theory), maybe then resources can be pooled and the issue finally solved.